Method and apparatus for determining eye topology

ABSTRACT

A method and apparatus for measuring the topography of the corneal and scleral regions of the eye. The measurements provide surface contours that are useful in the manufacture of scleral contact lenses.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/654,151 filed Oct. 17, 2012 which is a non-provisional ofSer. No. 61/547,904 filed Oct. 17, 2011.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention generally relates to a method and apparatus for makingoptical measurements and more specifically to a method and apparatus formeasuring the topography of an eye particularly over the regions of thecornea and sclera.

Description of Related Art

Accurate knowledge of the surface shape or “topography” of a patient'seye is essential to a number of ophthalmic procedures, examinations anddiagnoses of the eye, such as cataract procedures, Lasik procedures andthe manufacture of properly fitting, optically functional, comfortablecontact lens. In all these applications information about the topographyof the cornea and sclera is particularly important. In regions where alens contacts the eye, including regions under the eyelids, preciseknowledge of eye topology greatly facilitates manufacturing the lens insuch a way as to achieve optimal rotational orientation and patientcomfort. However, measuring eye topology, and more specifically that ofthe cornea and sclera, is complicated by the steep curvature of the eyein the scleral region, eyelid obstruction of the upper and lower scleralregions, and random eye motion during the measurement procedure.

Prior art apparatus incorporating Optical Coherent Tomography (OCT) andPlacido Rings technology and currently used to measure eye topology havevarious limitations with respect to acquiring measurements that can beused to construct an accurate model of an individual's eye. Placido Ringtechnology, for example, operates by projecting a series of concentricrings onto the surface of the eye and measuring ring placement anddistortion to determine surface topology. However, this technology doesnot provide sufficient and accurate information due to surfaceirregularities along the rotational axis of the projected ring.Consequently information can be lost if the rings merge together due toirregularities in eye surface topology. Resolution is limited in theradial direction due to a small number of rings, on the order of 22, andsurface topology cannot be measured under the eyelids. OCT operates byacquiring a temporal series of height profile cross sections of the eyescanned at different angular positions around an axis normal to thefront surface of the pupil. To create a three-dimensional model of theeye multiple cross sections must be scanned without the eye moving andthen accurately combined maintaining strict alignment between thescanned cross sections. Unfortunately, if the eye moves during orbetween successive sequential cross sectional measurements, the modelwill be inaccurate, because there is no way to reference each crosssection to a fixed spatial reference on the patient's eye. In addition,cross sections are currently limited to approximately 16 mm in diameterdue to the steep curvature of the sclera. A 16 mm diameter image isinsufficient to incorporate the wide scleral contact lenses withdiameters up to 22 mm. Moreover, OCT and Placido Ring scanners are notreadily adapted to measure scleral topology under an individual'seyelids.

U.S. Pat. No. 5,493,109 to Wei et al. (hereinafter “Wei-109”) disclosesOCT apparatus with an ophthalmologic surgical microscope. Automaticfocusing is provided by driving a motorized internal focusing lens ofthe ophthalmologic surgical microscope with a signal output from the OCTapparatus. An embodiment of such a system includes: (a) opticalcoherence tomography apparatus; (b) a beam combiner for internallycoupling output from the OCT apparatus into the ophthalmologic surgicalmicroscope; and (c) a motor for moving an internal focusing lens of theophthalmologic surgical microscope in response to a signal from the OCTapparatus.

U.S. Pat. No. 6,741,359 to Wei et al. (hereinafter “Wei-359”) disclosesOCT apparatus and describes the particular methodology and limitationsof the system described in Wei-109. Wei-359 discloses one embodiment ofa scanner for a beam of scanning OCT radiation that includes: (a) asource of OCT radiation; (b) a scanner; and (c) scanning optics in whichan image surface has a negative field curvature. As disclosed, Wei-109is limited to scanning the corneal region of the eye. This systemutilizes a large aperture and auto-focusing to meet the depth of fieldparameters of the cornea. As a result, and as described later, thisprocess also affects the light collection efficiency of the system. InWei-359 custom optics focuses a beam of OCT radiation in a curved arcthat approximates that of the human cornea. The object is to confine OCTradiation to be parallel to the surface of the eye. Such a systemproduces depth profile information along user-programmed radial scanlines that traverse the diameter of the eye. As a practical matter sucha system appears limited to measurements of the corneal region andunable to cover the corneal and entire sclera regions.

Recently attempts have been made to manufacture “scleral lenses” forindividuals whose corneas were damaged or deformed by accidents, such asexplosions, or who are diagnosed with Keratoconus, a disease that causesthe central area of the cornea to thin and bulge outward. Asconventional contact lens sit on the corneal surface, they are notappropriate for such individuals. However, scleral contact lenses reston the sclera and not the deformed cornea. Consequently such scleralenses have been used to restore vision to many patients. The lens worksby creating a new optical surface that is raised above the damagedcornea. The gap between the back of the lens and corneal surface fillswith the patient's own tears creating a pool of liquid tears that act asa liquid bandage to soothe the nerves on the corneal surface. The newlyformed rigid front optical surface of the lens then focuses lightthrough the patient's eye onto the back retina to restore vision. Toachieve the best optical performance with optimal patient comfort, thescleral lens must perfectly match the shape, curvature, and topology ofthe patient's sclera, which is the bearing surface of the lens includingthe bearing regions under the eyelids.

Prior art measurement apparatus, such as OCT apparatus, is not anoptimal choice for making such measurements due to their limitedscanning diameter and area. That is, such prior art measurement systemscannot reach sufficiently far into the sclera where the lens contactsthe eye. Moreover, a human eye often has a toric shape so the long andshort axes not necessarily at 0° and 90°. Toric eye profile informationalso needs to be computed to achieve optimal fit. Prior art systems donot measure the toricity of the sclera or provide the scan orientationof the long and short toric axes.

This lack of measurement capability has limited the use of sclera lens.Currently, it is necessary to manufacture a set of trial lenses to allowa physician to determine the most comfortable lens in the set, much likefinding the best shoe size that fits a customer's foot without evenhaving a ruler to first measure foot size. As will be apparent, fittingscleral lenses is very time consuming, can only be performed by a fewspecially trained doctors and trained personnel, requires skilledpersonnel at all phases and is very expensive.

SUMMARY

Therefore, it is an object of this invention to provide a method andapparatus for providing accurate measurements of the topography of theeye.

Another object of this invention is to provide a method and apparatusfor providing accurate measurements of the topography of the corneal andscleral regions of the eye.

Still another object of this invention is to provide a method andapparatus for providing accurate measurements of the topography of thecorneal and scleral regions of the eye that takes into account thetoricity of the scleral region.

Yet another object of this invention is to provide a method andapparatus for minimizing and simplifying the effort for making scleralcontact lenses.

Yet still another object of this invention is to provide a method andapparatus for minimizing and simplifying the process for determining thetopography of the eye.

Still yet another object of this invention is to provide a method andapparatus for minimizing and simplifying the process for determining thetopography of the corneal and sclera regions of an eye.

Yet still another object of this invention is to provide a method andapparatus for measuring the toricity of the sclera automatically, forcomputing the long and short toric axes automatically and for scanningthe eye automatically to provide profile information along the two toricaxes.

Yet still another object of this invention is to provide a method andapparatus for creating a three dimensional model of the eye in thescleral-corneal region.

In accordance with one aspect of this invention, an apparatus formeasuring the topography of the surface of an eye characterized by atleast one distinct visual feature includes a camera, a scanner and acontrol. The camera is aimed along an imaging axis for capturing atwo-dimensional image of the eye's surface including at least onedistinct visual feature. The scanner generates distance informationcorresponding to the distances from an internal reference to the surfaceof the eye at a plurality of positions along each of a plurality ofspaced scan lines during a scanning operation. During this scanning, afixed spatial relationship is maintained between the camera and thescanner. The control connects to the camera and the scanner. Itfunctions to: (1) control the scanner to produce at least one scan alonga scan line during a scanning operation thereby to obtain a plurality ofdistances at the along a scan line, (2) to cause the camera to captureat least one eye image during each scan, and (3) to store, for eachscan, the distance information obtained by the scanner and thecorresponding captured image information from the camera. A processingmodule combines the distance information from each scan line and thecorresponding captured image information thereby to obtain an accuraterepresentation of the topography of the eye.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims particularly point out and distinctly claim thesubject matter of this invention. The various objects, advantages andnovel features of this invention will be more fully apparent from areading of the following detailed description in conjunction with theaccompanying drawings in which like reference numerals refer to likeparts, and in which:

FIG. 1 depicts a simplified cross section of an eye;

FIG. 2 is a mathematical representation of an eye useful inunderstanding aspects of this invention;

FIG. 3 is a representation of an eye and imaging optics useful inunderstanding certain aspects of this invention;

FIG. 4 is another representation of an eye and imaging optics useful inunderstanding other aspects of this invention;

FIG. 5 is still another representation of an eye and imaging opticsuseful in understanding still other aspects of this invention;

FIG. 6 is a cross section of an eye and with a representation of ascleral lens that is useful in understanding aspects of this invention;

FIG. 7 is a cross section of the eye of FIG. 6 with annotations that areuseful in understanding this invention;

FIG. 8 is a cross section of the eye of FIG. 6 with a functional view ofa first embodiment of apparatus incorporating this invention;

FIG. 9 is a functional view of imaging optics useful in understandingthis invention;

FIG. 10 is a simplified block diagram of one implementation of eyescanning apparatus that is used as a profile measurement unit and thatincludes features of this invention;

FIG. 11 is a block diagram of another implementation of a profilemeasurement unit;

FIG. 12 is a block diagram that is useful in understanding aspects ofthis invention;

FIG. 13 is a block diagram of a system implementation that incorporatesthis invention;

FIG. 14 is an image of an animal eye annotated to disclose regions ofinterest;

FIG. 15 is a graph of the signal from the scleral region generated byapparatus incorporating this invention during a scan of the eye in FIG.14;

FIG. 16 is a graph of the signal from the limbus region generated byapparatus incorporating this invention during a scan of the eye in FIG.14;

FIG. 17 is a graph of the signal from the corneal region generated byapparatus incorporating this invention during a scan of the eye in FIG.14;

FIG. 18 is a graph of the signal from the corneal and pupil regionsgenerated by apparatus incorporating this invention during a scan of theeye in FIG. 14;

FIG. 19 schematically depicts the organization of a second embodiment ofapparatus incorporating this invention;

FIG. 20 schematically depicts a third embodiment of apparatusincorporating this invention;

FIG. 21 depicts a fourth embodiment of apparatus incorporating thisinvention;

FIG. 22 depicts a fifth embodiment of apparatus incorporating thisinvention;

FIG. 23 depicts a sixth embodiment of apparatus incorporating thisinvention;

FIG. 24 depicts a seventh embodiment of apparatus incorporating thisinvention;

FIG. 25 is a schematic view that is useful in understanding thisinvention;

FIG. 26 is a block diagram of eye scanning apparatus constructed inaccordance with this invention;

FIG. 27 is a schematic view of a control system that is useful with theeye scanning apparatus in FIG. 26;

FIGS. 28, 29 and 30 are useful in understanding the generation of eyetopography in accordance with one aspect of this invention;

FIG. 31 is schematically depicts apparatus for obtaining a fullycontoured model of the eye;

FIG. 32 is useful in understanding toricity of the eye;

FIG. 33 is an example of an image of an eye obtained in accordance withcertain aspects of this invention as might be used by anophthalmologist;

FIGS. 34 and 35 are images of an eye and the range of coverage obtainedwith OCT apparatus;

FIG. 36 is an example of how an OCT system can be modified to obtaingreater coverage of the eye; and

FIGS. 37A and 37B are helpful in understanding apparatus that might beused to extend the effectiveness of OCT apparatus.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1 through 6 are useful in understanding the prior art and thelimitations of the prior art when applied to determining, with accuracy,the topography of the corneal and scleral regions of any eye,particularly when the information is to be used in the manufacture ofscleral lenses. It is difficult to image surface regions, such as thesclera region of the eye with its steep curvature. FIG. 1 depicts an eye29 in cross section. When an incident light beam 30I from a sourceimpinges perpendicularly upon the surface of the cornea 31 and retina32, it is reflected and scattered back toward the imaging optics asindicated by reflected light beams 30R and 30R′. However, when anincident light beam 341 impinges upon the steep area of the sclera 33,most light is reflected and scattered away from the imaging optics as adirectly reflected beam 34R because the angle of incidence α must equalthe angle of reflection. Scattered light appears as quasi-directionalscattered beams 34Q and off-axis scattered beams 34O. The small amountof light energy reaching the prior art apparatus is insufficient toprovide any meaningful information about the surface topology of thesclera 33.

A second limitation is the reduction of the signal-to-noise ratio (i.e.,image quality) and the lateral resolution of an image which occurs whenthe optical depth of field is increased to image objects with greaterheight or depth. FIGS. 2 and 3 illustrate the graphical relationshipbetween the optical depth of field (DOF) and the diameter (DIA) of aregion of the eye 29 imaged by OCT apparatus. Equations (1) and (2)describe mathematically to what extent the depth of field (DOF) must beincreased to accommodate a larger image diameter.

$\begin{matrix}{{DIA} = {2*\sqrt{R^{2} - \left( {R - {DOF}} \right)^{2}}\mspace{14mu} {and}}} & (1) \\{{DOF} = {R - \sqrt{R^{2} - \left( \frac{DIA}{2} \right)^{2}}}} & (2)\end{matrix}$

-   wherein DIA=the maximum measurable diameter, DOF=the depth of field,    and R=the approximate radius of the eye ball.    As known, however, increasing the depth of field (DOF) requires a    decrease in the numerical aperture (NA) of the imaging optics and,    as also known, NA² is a measure of the amount of light or signal    collect by the imaging optics.

FIG. 3 depicts an imaging lens 35 for imaging the eyeball 29 whichexhibits a depth of field (DOF) and maximum measurable diameter(DIA_(max)) that can be measured for that depth of field. As also known,NA is given by:

$\begin{matrix}{{NA} = \sqrt{\frac{\lambda}{2*{DOF}}}} & (3)\end{matrix}$

wherein λ=illumination wavelength, and NA=imaging optics numericalaperture. As will be apparent, this relationship has adverse effects.First, decreasing NA reduces the lateral resolution by increasing thesize of the minimum detectable feature (RES) given by:

$\begin{matrix}{{RES} = \frac{\lambda}{2*{NA}}} & (4)\end{matrix}$

Decreasing NA also reduces light collection efficiency and the lightcollection cone angle of the optics given by:

Light Collection Efficiency≈NA ²  (5)

and

Light Collection Cone Angle θ=2*sin⁻¹(NA)  (6)

To better understand the effects of reducing the light collection coneangle, consider imaging optics with a cone angle 36 in FIG. 4 andsmaller cone angle 36′ in FIG. 5. Incident beams 37I and 37′I of lightimpinging upon the curved surface of an eye 29 reflect along beams 37Rand 37′R, and scatter along beams 37S and 37'S, in some combination.When the reflected and scattered light falls within the collection coneangle 36 of the imaging optics, as shown in FIG. 4, this light iscaptured by the imaging apparatus. With a smaller cone angle 36′ in FIG.5, light falls outside the collection cone angle and is not captured bythe optics and cannot provide any information regarding surfacetopology.

FIGS. 4 and 5 also depict the relationship between cone angle and depthof field wherein a depth of field 36 DOF in FIG. 4 is less than thedepth of field 36′ DOF in the system with the smaller cone angle 36′.

Table 1 (below) lists the light collection cone angle, depth of focus(DOF), maximum prior art image diameter, resolving power, and lightcollection efficiency, as a function of the numerical aperture of theprior art imaging optics.

TABLE 1 Optical Parameters (Eyeball diameter of 24.5 mm) Depth ofResolving Numerical Light Collection Cone Angle Focus$\frac{\lambda}{2*{NA}^{2}}$ Maximum OCT Image Power for$\frac{\lambda}{2*{NA}}$ Light Aperture (degrees) λ = 0.55 μ Diameter λ= 0.55 Collection Efficiency (NA) θ = 2xsin¹(NA) (mm) (mm) (microns)(NA²) 0.08 9.17 0.04 2 3 6875 × 10^(−6—) (275x) 0.04 4.58 0.16 4 6 1718× 10^(−6—) (68x) 0.03 3.43 0.37 6 9 743 × 10^(−6—) (29x) 0.02 2.29 0.678 13 410 × 10^(−6—) (16.4x) 0.016 1.83 1.06 10 17 259 × 10^(−6—)(10.36x) 0.012 1.37 1.57 12 20 144 × 10^(−6—) (5.76x) 0.01 1.14 2.5 1425 100 × 10^(−6—) (4x) 0.009 1.03 3.0 16 27 81 × 10^(−6—) (3.24x) 0.0080.91 3.9 18 31 64 × 10^(−6—) (2.56x) 0.007 0.80 5.17 20 37 49 × 10^(−6—)(1.96x) 0.006 0.68 6.86 22 41 36 × 10^(−6—) (1.44x) 0.005 0.57 9.75 2450 25 × 10^(−6—) (1x)

Table 1 further illustrates how problematic it can be to image a curvedsurface. For example, a lens with a numerical aperture of 0.08 has alight collection cone angle of 9.17 degrees but only has a depth offield (DOF) of 0.04 millimeters (40 microns). Therefore the curvedsurface rapidly goes out of focus as the eye is scanned. This smalldepth of field can be increased to 9.75 millimeters by using a lens witha numerical aperture (NA) of 0.005, but this reduces the collection coneangle to a miniscule 0.57 degrees. Therefore as the curvature of the eyebegins to increase, the reflected and scattered light beams quickly falloutside the cone angle of the imaging optics. Moreover, the totalcombined reflected and scattered light collected by the imaging opticsof a system is proportional to NA². Therefore, reducing the NA from 0.04to 0.005, for example, reduces the amount of collected light by a factorof 275. Consequently measurements for determining the surface topologyof an individual's eye with prior art systems are difficult, if notimpractical.

With this as background, FIGS. 6 and 7 are illustrations of a human eye29 with its cornea 41, sclera 42, anterior chamber 43, iris 44, lens 45,vitreous body 46, retina 47 and limbus 48 at the boundary of the cornea41 and the sclera 42. FIG. 6 depicts a lens 50 that rests on the sclera42. The requirements for a system to measure the topography of both thecorneal and scleral regions of the eye in FIGS. 6 and 7 should include amaximum profile diameter of 24 mm with a depth of field of 12 mm.Moreover the system must be sufficiently fast to prevent eye motion fromadversely impacting the acquisition of the data during a scan.

As shown in FIG. 1, when the eye 29 is illuminated by an apparatus froman angle perpendicular to the surface of the cornea 41 (i.e., verticallyin FIG. 1) the light angle of incidence and reflectance rapidlyincreases as one laterally scans across the sclera 42 toward the outerextremities of the eye. If, however, one views the eye from an angle andoff to the side relative to the top of the corneal surface, the outerregions of the cornea 41 and sclera 42 can be shown to lay along dashedtangent lines 51 and 52 as indicated in FIG. 7.

Now referring to FIG. 8, one method for measuring the curvature of thesclera 42 and the cornea 41 involves establishing a “tangent” line 50 or51 at the surface of the eye overlying portions of the cornea andadjacent sclera and placing a source 53 or a source 54 for an opticalbeam onto a linear track with the beam oriented at a given angle (A)relative to the dashed tangential lines 51 and 50 respectively. It hasbeen found that an angle of 27°<β<47° relative to an axis perpendicularto the top of the pupil provides improved results. A value of about 37°has been used successfully. Functionally, as each of the sources 53 and54 moves away from the eye along a track through positions 1 to 7, thecorresponding incident beam laterally traverses across the surface ofthe eye moving from the outer extremes of the sclera 42 toward and ontothe cornea 41. Throughout the entire duration of the scan the angles ofthe incident beam, reflected and scattered beams remain approximatelythe same, varying only slightly due to small perturbations in thesurface of the eye.

Referring to FIG. 9, when an incident beam 57I impinges upon the surfaceof the eye at a position along a tangent line, such as tangent line 51and the eye 29 is scanned in a direction represented by an arrow SD, thelight beams returning from the surface are composed of a directlyreflected component 57R and multiple scattered components 57S which intotal form an oval shaped spatial distribution of optical energyreferred to as the surface's Bidirectional Reflectance Function. In aspecific embodiment of this invention the angles of the incident beamand imaging optics are optimized to collect the strongest signal forscanning of the sclera and corneal regions.

FIGS. 10 and 11 show the use of telecentric and non-telecentric optics,respectively, to collect the directly reflected and quasi-directionalscattered light beams from an eye and to provide a distance measurementusing triangulation. FIG. 10 depicts an integrated measurement unit 60which packages an incident light beam source 61 and a camera withtelecentric imaging optics. FIG. 11 depicts another embodimentcomprising an integrated measurement unit 63 with an incident light beamsource 64 and a camera 65 with non-telecentric imaging optics 66.

It is important that the data acquired from all radial measurements bespatially aligned to each other and to the same known spatial positionin the eye. Therefore, as is true in many measurements of the eye, theeye should not move during the data acquisition process. It has alsobeen reported that torsional saccades of 5 or 10 degrees mayoccasionally occur even during steady fixation.

When measuring the profile, it is useful to know the approximatelocation of the limbus 48 shown in FIG. 7 to calculate the optimallocation at which the contact lens should lift or begin to raise abovethe sclera 42. However, obtaining an accurate smooth topology map isvery difficult because the optical light reflection and scatteringproperties (Bidirectional Redistribution Functions) of the sclera 42 andcornea 41 are different. The sclera 42 is white with a shiny surfacewhich produces a relatively strong reflected and directionally scatteredsignal. In comparison, the cornea 41 is clear and designed by nature totransmit, not reflect, light; therefore both the directly reflected anddirectionally scattered optical components from the cornea 41 arerelatively weak.

Camera signal output when viewing different regions of the eye is givenby the equation:

Cam_(sig)≈[(ILLUMIN*REF*TIME_(INTEGRATION) *NA ² *K)+NOISE]*Eg]  (7)

wherein:

-   ILLUMIN=total illumination power incident on the eye REF=the percent    of illuminated light either reflected or scattered off the surface    of the eye being scanned and is given by:

$\begin{matrix}{{REF} = \frac{\left( {{REFLECTED} + {SCATTERED}} \right){LIGHT}\mspace{14mu} {INTENSITY}}{{ILLUMINATION}\mspace{14mu} {LIGHT}\mspace{14mu} {INTENSITY}}} & (8)\end{matrix}$

-   TIME_(INTEGRATION)=time duration over which light is collected by    the camera-   NA²=the (numerical aperture) of the imaging optics and is a measure    of how much of the reflected and scattered light is collected by the    imaging optics-   K=optical power to electronic signal conversion constant for the    camera,-   NOISE=electronically introduced noise of the camera electronics when    viewing a dark field, and-   Eg=electronic gain or amplification of the camera signal.

Equation (8) can be expressed in terms of optical gain (Og) andelectronic gain Eg, such that:

Cam_(sig)≈[(REF*Og)+NOISE]*Eg  (9)

where

Og=[ILLUMIN*REF*TIME_(INTEGRATIoN) *K)]  (10)

Qualitatively, from equation (9):

-   -   [Og×Ref]>NOISE in order to detect signals from the scanned        region of the eye,    -   Increasing electronic gain, Eg, increases the magnitude of the        NOISE in the camera output signal, and    -   Increasing electronic gain Eg does not improve the signal to        noise ratio as:

$\begin{matrix}{{S\text{/}N} = \frac{{Og}*{REF}}{NOISE}} & (11)\end{matrix}$

When scanning the sclera 42, its smooth white surface returns much ofthe illumination beam to the camera creating a strong electronic signalso both the optical gain, Og, and electronic gain, Eg, can be kept atminimal levels. This implies the use of minimal illumination power sinceoptical gain OG is proportional to illumination intensity. Incomparison, detection of the surface of the cornea 41 requires muchgreater optical and electronic gain due to the weakly reflected andscattered signal levels from the cornea. Detection of the cornealsurface is further complicated because the camera simultaneouslyreceives two signals, a weak signal from the cornea and a much strongersignal from the underlying iris, as shown in FIG. 12.

Referring to FIG. 12, when a source is at location 81, its incident beam84 strikes the sclera 42 and reflects and scatters a strong signalrepresented by beam 85 back toward the camera. When the illuminationbeam scans over the cornea 41 with the source at location 80, the sourcebeam impinges upon the surface of the cornea 41 and only a smallpercentage of the power is reflected and scattered back to the camera asshown by beam 82. The majority of the power transmits through the corneaas shown by illumination beam 83 impinging upon the surface of the iris44, which in turn reflects and scatters a much stronger signalrepresented by beam 84 back toward the camera. It will also be observedfrom FIG. 12, that the spatial locations of the beams imaged onto thecamera from the cornea and iris are different. However, since both beamssimultaneously strike the camera, a profile measurement unit mustcontrol both the electronic gain (Eg) and optical gain (Og) in real timeas the eye is scanned spatially and in real time as the signal is readout of the camera for a given spatial position along the cornea.

In accordance with this invention, in essence each signal peakrepresenting the sclera, cornea, and iris has the electronic gain andoptical gain automatically optimized for processing of the signal.Optical gain is adjusted by varying the camera integration time(TIME_(INTEGRATION)), illumination power (ILLUMIN) and illuminationpulse width (PW). A Master Signal Control Module 90 shown in FIG. 13provides such optimization. The Master Signal Control Module 90 includesa camera signal analyzing module 91 which has the capability ofcontrolling illumination power and pulse width from a source 92 throughan illumination control module 93. The analyzer module 91 also adjustscamera or optical sensor integration time through control module 95, andthe magnitude of the camera output which is fed to an amplifier 96 underthe control of electronic gain control 97.

More specifically, such a master signal control module 90 can beimplemented as follows:

-   A. Predetermined minimum and maximum values are set for the    electronic gain, Eg in the module 97, camera integration time    (TIME_(INTEGRATION)) in the module 95, illumination intensity    (ILLUMIN) and illumination pulse width (PW) in the module 93 such    that:-   Eg_(min)≦Egg≦Eg_(max)-   TIME_(INTEGRATIONmin)≦TIME_(INTEGRATION)≦TIME_(INTEGRATIONmax)    -   IL_(min)≦ILLUMIN≦IL_(max)-   PW_(min)≦PW≦PW_(max)-   B. Referring to FIGS. 12 and 13, when the sclera 42 is scanned, a    strong signal is received. When this occurs, the modules 97, 95 and    93 set Eg, TIME_(INTEGRATION) and Pw to minimal values via the    feedback loop provided by the analyzer 91 that monitors the camera    or optical sensor signal level.-   C. When the scan reaches the Limbus 48, the weakly returned signal    from the cornea 41 immediately causes electronic gain Eg and Optical    Gain (Og) to be increased.-   D. When a scan reaches the iris 44, the stronger signal from the    iris 44 is examined, temporally later in the same camera output    line, and the optical and electronic gains are reduced.

As previously stated, optical gain is a function of: integration time,illumination pulse width and illumination power variables. The order inwhich these variables are increased and decreased is programmable. Thereadout time of the camera or optical sensor and processing time of theMaster Signal Control Module 90 FIG. 13 must be very fast relative tothe spatial scan rate of the profile measurement units to insure thatmultiple measurements of repetitive data can be read out of the cameraand the various parameters adjusted while the camera or optical sensoris still looking at the same position on the eye.

Each Profile Measurement Unit can be implemented using individualcomponents or by using a laser displacement sensor. Such sensorsincorporate a laser illumination source, a high speed CMOS camerasensor, and electronics to adjust the illumination power, illuminationpulse width, sensor integration time, and sensor gain in real time andto provide distance at successive locations along a scan line. Such asensor was incorporated into a Profile Measurement Unit configured inaccordance with the optical, mechanical, electronic, and processingparameters described above to enable detection of the sclera, Limbus,and corneal regions of a pig eye as shown in FIG. 14. The pig eye wasplaced in a dish and scanned with one Profile Measurement Unit. FIG. 15shows the detection of the sclera and its distance from the knownposition of the Profile Measurement Unit. FIG. 16 shows the detection ofthe Limbus, indicating the position of the cornea and the beginning ofthe iris. FIG. 17 shows signals from both the cornea and iris, and FIG.18 shows signals from the cornea and pupil. The underlying data fromwhich these graphs were plotted can then be assimilated to createsurface contours of the scleral and corneal regions of the eye.

It has been found that a source beam is of shorter wavelength, such asblue light, will produce a greater percentage of light that is reflectedand scattered toward the optical sensor than for a source beam of alonger wavelength such as red light. Experiments have demonstrated thatred light reflected from the cornea is 208/(256+208)×100%=45% and thelight reflected from the iris=256/(256+208)×100%=55% indicating thatmore light is reflected from the iris than from the surface of thecornea. If the cornea were to become very thin, as with Keratoconispatients, the two reflected red beams will spatially move together onthe surface of the optical sensor making it difficult to accuratelydetect the spatial position of the thin cornea. When the cornea isilluminated with the shorter wavelength blue light the cornea reflects180/(72+180) x=72% of the light and the iris reflects 28%. The signalfrom the cornea is 2.5 times stronger than the signal from the iris tofacilitate detection of the corneal surface.

Referring again to FIGS. 8, 10 and 11, this system includes an imagingunit and optical source. In FIG. 8 the optical source moves along a path53 while directing illumination from the source to the eye 29essentially normal to the tangent line 51. In FIGS. 10 and 11 theintegrated source/optical sensor moves along path 53 while directingillumination from the source to the eye 29 essentially normal to thetangent line 51. During each scan, it is necessary to move the source inFIG. 8 and integrated source measurement units 60 and 63 in FIGS. 10 and11. The components of such an integrated measurement 60 or 63 produce astructure with significant weight with attendant mass and inertiaproblems that arise when moving such structures rapidly over a shortdistance. This may limit the ability of such apparatus to attain all ofthe benefits of this invention.

FIG. 19 depicts an alternative embodiment of a triangulation measurementunit 120 that includes an optical beam source 121 and camera and imagingoptics 122. As these components are contained within unit 120, theyundergo no motion during a single scanning operation relative to themeasurement unit 120. Illumination from the optical beam source 121 isdirected to an extremely lightweight scanning minor 123 contained withinmeasurement unit 120. The scanning mirror undergoes an angulardisplacement of ±θ/2. Light energy reflecting from the minor 123 isdirected to a theta lens 124. As known in the art, a theta lensredirects light received along different axes from a source such as thescanning mirror 123, along parallel axes as shown by dashed lines 125between the theta lens 124 and the tangent line 51 at the eye 29. Thisillumination pattern has the same characteristics as the pattern of FIG.8, but in this embodiment the only moving element is the scanning mirror123 that has minimal weight.

As another alternative triangulation unit, FIG. 20 discloses anintegrated measurement unit 130 with a fixed optical beam source 131 andcamera and imaging optics 132, but without a theta lens. In thisconfiguration, the light is transmitted from a mirror 133 directly alongthe lines 136 as they travel from the minor 133 to the tangent plane 51as the scanning mirror 133 rotates through its operating angle. Atreasonable measurement ranges, it may be possible to scan the cornea andsclera of an eye by moving the scanning mirror through a limited rangeof motion (e.g., ±5° for a measurement distance of 100 mm away from theeye). As previously indicated, the reflected light from the cornea andsclera acts according to a Bidirectional Reflection Function (FIG. 9).Consequently, over a small angular range of scanning mirror motion theimaging optics should be able to collect a strong signal over the entirescan segment of the eye without significant variation or error. Such aconfiguration, while not producing an illumination beam as parallel tothe tangent as the theta lens system of FIG. 20, minimizes or eliminatesthe need for the theta lens and its attendant support structures therebyreducing the number of optical components in the unit 130 and theoverall weight of the unit 130. Weight of the measurement unit is aconsideration when constructing apparatus for revolving the measurementunit 130 about the eye to allow successive scans to be taken andangularly displaced locations.

FIG. 21 depicts still another measurement unit 140 variation wherein thepositions of the scanning minor and the camera and imaging opticschange. The integrated measurement unit 140 includes an optical beamsource 141 that directs light to scanning minor 142 and through a thetalens 143. The theta lens 143, in turn, redirects light along parallelpaths 144 to intersect the tangent line 51 at an oblique angle in therange of about 27° to 47° relative to an axis perpendicular to the topof the pupil; in one embodiment the angle is selected to be about 37°.Light reflected from the eye 29 travels nominally along parallel paths145 to camera and imaging optics 146.

Referring to FIGS. 19 and 21, in FIG. 19 the camera optics depth offield (DOF) must be sufficient to provide focus over all theintersections of the light rays between the outer illuminating rays 125with the eye surface proximate the tangent line 51. The apparatus FIG.21 minimizes the depth of field requirements because all the reflectiveeye surfaces of interest (e.g., portions of the cornea, the sclera andlimbus) lie in a narrow range of distances from the camera and imagingoptics 146.

The configuration of FIG. 22 provides a similar advantage over theconfiguration of FIG. 20. In FIG. 22 an integrated measurement unit 150includes an optical beam 151 that directs light to a scanning mirror 153which, in turn, redirects light along the angularly displaced path lines154 toward the eye surfaces along the tangent line 51. Light reflectsand is scattered back from the illuminated portions of the sclera,cornea and limbus to the camera and imaging optics 152 along lines 155to obtain meaningful data. Again as the camera and imaging optics 152are oriented to receive light reflected along lines 155 that are normalto the tangent 51, the required depth of field for the optics in FIG. 22is significantly reduced as compared to the depth of field requirementfor FIG. 20.

FIG. 23 depicts an alternate version of the measurement unit 160 whichincludes a triangulation sensor 161 with an integrated illuminationsource 162 and an optical position sensor 163. The illumination source162 directs a beam to a scanning minor 164 that a motor drive 165oscillates about a narrow angular range (e.g., ±0°). As the illuminationbeam from the illumination source 162 is scanned across eye 29, it isreflected and scattered toward the scanning mirror and back to theoptical position sensor. It is displaced on the position sensor, such asat points “a”, “b” and “c” as scanning mirror 164 oscillates on a shaft167 and corresponding axis. In FIG. 23 the long axis of the scanningminor and the long axis of the integrated source beam—optical sensortriangulation unit are perpendicular to the plane of the page. As thesource beam scans the meridian along the tangent line, drawn in theplane of the page, the orientation of the optical position sensor withinthe triangulation unit and hence light rays corresponding to beams “a”,“b” and “c” are perpendicular to the direction of the page.

In FIG. 24 a measurement unit 170 includes a position sensor 171 with anintegrated illumination source 172 and an optical position sensor 173.The illumination source 172 directs a beam to a scanning mirror 174 thata motor drive 175 oscillates about a narrow angular range (e.g.,θ≈+/−5°). As this illumination beam scans a meridian across the eye, thereflected and scattered light from the eye 29 is directed toward theoptical position sensor by scanning mirror 174 and is displaced on theposition sensor, such as at points “a”, “b” and “c” as scanning minor174 oscillates on a shaft 177 and corresponding axis. In FIG. 24 thelong axis of the scanning minor (shown as line 174) and the long axis ofthe integrated source beam-optical sensor triangulation unit are withinthe plane of the page. As the source beam scans the meridian along thetangent line, drawn in the plane of the page, the orientation of theoptical position sensor within the triangulation unit and hence lightrays corresponding to beams “a”, “b” and “c” are also within the planeof the page. The imaging lens within the position sensor captures thelower magnitude out of plane light rays within the cone angle of theimaging optics

The position sensor 161 in FIG. 23 and the position sensor 171 in FIG.24 incorporate triangulation sensors that incorporate a structure andoperation that processes the optical light rays based, in part, on theSchleimpflug theory, such as incorporated in the Micro Epsilon ModeloptoNCDT1700 BL series or optoNCDT2300 BL series, each of whichincorporates a blue laser. The triangulation 161 and 171 may alsoinclude a red laser for some applications although a blue laser appearsto provide better results when measuring biological material such asfound in the eye.

Scanning minor assemblies such as with scanning mirror 164 and mirrormotor 165 in FIG. 23 and the scanning minor 174 and motor 175 in FIG. 24are available from Cambridge Technology and are repeatable to 10micro-radians which is sufficient to provide a lateral resolution of 12microns with scan speeds that permit a 20 to 40 millisecond radian scantime; i.e. the time to make one scan across the surface of the eye fromabout the top of the eye across the cornea and the entire sclera (over ascan of a meridian). Such a configuration can measure the distance tothe cornea or sclera on eye 29, with a repeatability of 1 micron from100 mm away. It has been found that the optical position sensor 163 inFIG. 23 picks up beams scattered to the side. In FIG. 24, the opticalposition sensor 173 picks up beams that are both reflected and scatteredtoward the sensor in the relative plane of the page. As a result, theposition sensor 173 in FIG. 24 is less sensitive to signal degradationcaused by variations in eye surface texture and angle.

FIGS. 25 and 26 depict one embodiment of an eye-measuring apparatus 180for obtaining a high-resolution three-dimensional image of the eye. Thisapparatus 180 includes a platform 181 that rotates about an axis that issubstantially perpendicular to the optical axis of an eye 29 (parallelto the top front surface of the eye). Mounted on a fixed base (notshown) is a high-definition TV camera system 182 that monitors thepatient's eye position within a region 183 during each scan and that hassufficient resolution to determine the position of the eye 29 relativeto the position of a measurement unit 184 at different angularpositions. More specifically, in one embodiment, the platform 181rotates a single measurement unit, shown by solid lines 184 at aposition 1, and dashed lines at other positions around a patient's eye.The angular motion of rotation is indicated by arrows 185 in FIG. 25. Inthis particular case the system in FIG. 25 depicts the measurement unit184 at eight angular positions. As will be apparent, however, inpractice the number of positions can be much greater to achievenecessary sampling during a single scan operation during which theplatform rotates one revolution. It is expected that between 20 and 100angular positions will be measured during the scanning operation for asingle rotation of the platform 181 to achieve appropriate sampling fordifferent applications and ophthalmic procedures.

As shown in FIG. 26, a physical embodiment 200 of apparatusincorporating this invention includes a housing 201 with a frame thatdefines fixed spatial relationships between the TV camera 182 and themeasurement unit 170 or any of the other measurement unitimplementations. As previously indicated, the measurement unit 170generates distance information corresponding to the distances betweenthe internal reference position sensor 171 and the surface of the eye ata plurality of angular positions along each of a plurality of spacedscan lines during a scanning operation. In FIG. 26 the measurement unit170 is shown at two different locations during its rotation with theplatform 181 about an axis such as the viewing axis of the TV camera182. Rotation of the platform 181 is provided by a motor, typically aservo or stepping motor that is not shown but known in the art, toprovide a series of angularly spaced scanning positions at each of whicha single scan is taken. To obtain multiple scans during a scanningoperation, the measurement unit 170 rotates about the eye and at eachincremental position, defines a “meridian” along which the measurementunit 170 takes a meridian scan and obtains height information for thatmeridian.

FIG. 27 depicts one embodiment of a control system for the apparatus 200in FIG. 26 for interacting with the measurement unit 170, a scanningrotary stage corresponding to the platform 181 in FIGS. 25 and 26 andthe TV camera 182. A data acquisition, storage and control interfaceunit 202 interacts with the measurement unit 170, scanning mirror 176,rotary stage, such as the platform 181, and TV camera 182. Morespecifically, the data acquisition, storage and control interface 202activates the illumination source in the measurement unit 170, such as ablue laser, the scanning minor 176 and the position sensor in themeasurement unit 170 thereby to retrieve height data generated from thecorresponding optical position sensor including position data for eachheight measurement. The data acquisition, storage and control interface202 also sends signals representing command positions to the scanningmirror 176 and receives position feedback signals to allow accuratecontrol of the scanning minor angular position. Signals from the dataacquisition, storage and control interface 202 also control theoperation of the motor driving the rotary stage platform 181 or likesupport and receives encoded stage position signals representing theactual position of the rotary platform 181.

The TV camera 182 is constantly monitoring the patient's eye. Upon asignal from the data acquisition, storage and control interface 202, thevideo system “grabs” a picture of the eye and returns it to the dataacquisition, storage and control interface 202. Interaction andoperational control is provided through a user interface 203 thatincludes input and visual output capability and that interfaces withboth the data acquisition, storage and control interface and a highspeed image processor 204. The image processor 204 processes the heightsignals in combination with the image received from the TV camera toproduce the topography of that portion of the eye that has been sampledduring a single scan of the eye along a meridian and accumulates all thescan information made during one scanning operation.

Referring to FIG. 26, in some applications and prior to collecting data,a patient is instructed to look into the apparatus 200. A doctor oroperator causes the system to store a high resolution image of thepatient's eye using TV camera 182. Such an image would include all thefine features and details in the iris, features in the scleral regionsuch as blood vessels and the position and shape of the pupil. Inaddition, the physician or operator could identify a particular featurein the eye by various means to be used as a reference point. Then thesystem collects data along every meridian (i.e., eight equiangularlydisplaced meridians in FIG. 25). If the TV camera system detects any eyemovement during any meridian acquisition cycle, the data for the cycleis ignored and the eye can be rescanned at that meridian once the eyestops moving. With short data acquisition cycles, in the order of 20 to50 milliseconds or so, the system will produce a sequence of highresolution snapshots, one for each different position of the measurementmodule.

Each “snapshot” from the TV camera system will be accompanied by thecorresponding meridian height measurement data that defines the topologyof the eye along that scan line. That is, each meridian scan line, suchas the line 210 in FIG. 28 will have its own unique picture, shows themeridian scan line between points A and B which extends from the corneato the sclera 42, and the precise orientation of the meridian relativeto all the features in the TV image of the eye. FIG. 29 is a graphicalrepresentation of the relationship of the height measurements (from themeasurement apparatus) as a function of the radial distance along thesurface of the eye corresponding to the angular position of the scanningminor.

Once the measurement unit has rotated around the eye in a rotationalscanning operation during which multiple meridian scan are obtained, aTV image similar to that of FIG. 28 and height measurement data similarto that of FIG. 29 will exist for each measured meridian. It is thenpossible to process and combine the data from all the meridians toproduce an image of the eye for one orientation or starting position ofthe patient's eye. FIG. 30 graphically illustrates three such meridianscan operations for positions 1, 2 and 3, by way of example. Theindividual meridians, each consisting of a TV camera image withcorresponding height measurement data can then be combined to produce acomposite image for the rotational scanning operation. It has been foundthat such information can be processed by image-stitching software thatoverlays and superimposes each of the scans by stitching to spatiallyalign the meridian data as shown in FIG. 30 for all the meridians inthat scanning operation with the images of the eye in one orientation.Such composite images of the eye have been generated by the use ofAutopano image-stitching software available from Kolor SARL of France.

As previously stated, for a given orientation of an eye a portion of thesclera is covered by an eyelid. To scan the entire surface of the eye,including those regions normally covered by the eyelids different areasof a patient's eye can be scanned during a separate scanning operationfor each of different orientations of the patient's eye. FIG. 31discloses one approach in which a patient looks at a visual targetsequentially projected to center, upper, lower, left, and rightquadrants to expose the entire eye including the extreme anteriorscleral surface. That is, a complete measurement of the eye includesfive scanning operations, one for each of the eye positions at 210, 211,212, 213 and 214. The scanning operation 210 occurs when the patientlooking straight ahead. Each of the scanning operations at 211 and 212occur when the patient looks to the right and left respectively;scanning operations 213 and 214 occur when the patient looks up and downrespectively. Since the upper eyelid lowers as a patient looks down, aspeculum may be used to hold the eyelids open. Alternatively, the eyelidcan be taped to the patient's forehead prior to collecting data or heldup by the patient's finger or the finger of a doctor. An alternateapproach may avoid the need for taping the eyelids or using a speculum.Typically a patient will be scanned with the patient's chin on a chinrest or like positioning structure so that the patient's head remainsreasonably fixed. Such devices are known in the art. However, ratherthan projecting a target for viewing and aligning as previouslydescribed, a single target can be projected and then the patient canangularly rotate his or her head a small amount (e.g. about ±15°). Theeye will naturally rotate to a new position as shown in FIG. 31 as thepatient's head moves to keep the fixed target image in view.

By whatever means is used to obtain the images from multiple scanningoperations at different eye orientations, it is possible to process thedata for each scanning operation and stitch the data together to createa three-dimensional wide-field topology map of the eye using theabove-identified Kolor Autopano or like software. In addition, the humaneye is often toric in shape, like a foot ball, having two base curves,with a longer axis and a shorter axis, as shown in FIG. 32. The goal isto design a lens that matches this ocular surface, but this is difficultby conventional means because the scleral lens sits under the upper andlower eyelids. Toricity of the bearing surface can only be calculatedafter aligning and stitching together all meridians or cross sectionaldata as previously described.

FIG. 33 shows the information presentation that can be derived from thismethodology using such stitching software. Multiple images of anindividual's eye were taken with a TV camera and then stitched together.The result is the composite image 220 of the individual's eye. Thisimage is a graphical presentation of all the accumulated data from a setof scanning operations. The ring 221 represents a template which hasbeen manipulated on the image of FIG. 33 to define the boundaries of anarea of the sclera for supporting a sclera lens. Using conventionaltechniques a physician can manipulate the template of the ring to customalign the ring taking into account physical features of an eye. Thatinformation can be processed along the all the scan data to obtain amodel from which a sclera lens for that patient can be constructedefficiently.

As previously indicated, OCT scanners have been shown to be limited intheir ability to scan highly curved surfaces such as the sclera and needto be positioned relatively perpendicular to the top corneal surface.FIG. 34 depicts the image of an eye with a superimposed diameter lineC-D which corresponds to the extent of the OCT image shown in FIG. 35between the limits C and D. In the configuration shown in FIGS. 37A and37B, the topology scanner can either be a meridian scanner as describedabove or a conventional OCT type cross sectional scanner with an outputas shown in FIG. 35. FIGS. 37A and 37B illustrate a scannerconfiguration with an orientation close to perpendicular relative to thetop corneal surface. In this configuration the scanner tangent line isoriented at a shallow angle relative to the top surface of the cornea.As the eye rotates and fixates at different angular positions, differentregions of the eye become almost parallel with the tangent line and fallwithin the angular range of the topology scanner. For each position ofthe eyeball multiple meridians or cross sections are scanned. Eachscanned meridian or cross section is accompanied by a TV camera image.TV images with corresponding meridian height data for the differentpositions of the eye are then aligned to combine and reference allmeridians or cross sections to a fixed reference points in the eye tocreate a 3 dimensional model of the eye. FIG. 34 shows the camerapicture of an eye and the angular orientation of an OCT radial scanline, indicated by line C-D. FIG. 35 is the OCT image for radial scanline C-D. FIG. 36 illustrates how successive and multiple OCT scans arecombined using the same procedure previously described to combinemeridian data.

Each of the foregoing embodiments of this invention meets some or all ofthe various objectives of this invention. That is, the method andapparatus described above provide accurate measurements of thetopography of the eye, especially of the topography of the corneal,scleral and limbus regions of the eye taking into account the toricityof the scleral and corneal region. As a result, the method and apparatusof this invention can assist in minimizing and simplifying the effortfor making scleral contact lenses by minimizing and simplifying theprocess for determining the topography of the eye, particularly thetopography of the corneal and scleral regions of an eye including themeasurement of the toricity of the sclera and eye automatically, forcomputing the long and short toric axes automatically, for scanning theeye automatically to provide profile information along the two toricaxes, and to create an accurate three-dimensional model of the eye. Theapparatus is also useful in Lasik and cataract ophthalmic procedures toprovide accurate topology data of the corneal region.

This invention has been disclosed in terms of certain embodiments. Itwill be apparent that many modifications can be made to the disclosedapparatus without departing from the invention. For example, an OCTscanner might be modified by certain aspects of the invention. FIG. 35shows a full cross sectional image of an eye created by an OCT scanner.As shown, it includes the cornea and very top of the sclera near theLimbus but it does not show the steep regions of the sclera past theLimbus. Insertion of a beam splitter or dichroic minor into the opticalpath as shown in FIG. 37A enables the TV camera 182 to be offset so theoptical beams from the scanner and camera are both orientedperpendicular to the top of the corneal surface, as the eye looksstraight. In addition, when the viewing angles of the TV camera becomeclose to the beam angles of the meridian or cross section in an OCTscanner, insertion of a beam splitter or dichroic mirror into theoptical path can avoid mechanical interference between the two units. Ifthe measurement unit uses a monochromatic light source such as a bluebeam for example or a source outside the visible spectrum such as thenear IR wavelengths used in numerous OCT units the beam splitter can bereplaced with a dichroic minor to maximize power to the topology scannerand TV camera. Therefore, it is the object of the claims to cover allsuch variations and modifications as come within the true spirit andscope of this invention.

What is claimed is: 1.-14. (canceled)
 15. A method comprising generating an optical beam from a light source; scanning the optical beam to impinge a surface of an eye along a plurality of meridian scan lines of the eye; detecting, for a plurality of positions located along each meridian scan line, a reflected optical energy component, to thereby determine a set of distances for each meridian scan line; capturing, at the same time as the detecting step for each meridian scan line, a two dimensional visual image of the eye associated with the respective meridian scan line, to produce a set of two-dimensional images having a two-dimensional image for each meridian scan line; and aligning the set of two-dimensional images to generate a composite three-dimensional image of the eye, and to thereby also obtain a three-dimensional topography of the eye, and to thereby compensate the three-dimensional image and the three-dimensional topography for eye motion occurring during the scanning step.
 16. The method of claim 15 additionally comprising: scanning the optical beam along an axis that includes a line normal to a line tangent to a point on a sclera and to a point on a cornea of the eye.
 17. The method of claim 15 additionally comprising: placing, on a platform, an apparatus that performs the scanning, detecting, and capturing steps; and rotating the platform about an axis that is perpendicular to an optical axis of the eye.
 18. Apparatus as recited in claim 16 wherein the tangent line forms an angle between 27 degrees and 47 degrees relative to an axis perpendicular to a top of a pupil of the eye.
 19. The method of claim 15 additionally comprising: fabricating a lens from the three dimensional topography of the eye.
 20. The method of claim 15 additionally comprising: directing a patient to stare at a point of fixation while the patient angularly rotates their head to a different head position for each of a plurality of scanning steps.
 21. The method of claim 20 additionally comprising: stitching two-dimensional images obtained for two or more head positions.
 22. The method of claim 15 wherein the scanning step further comprises optical coherence tomography scanning.
 23. The method of claim 15 wherein the scanning step further directs illumination across a portion of the eye using an illumination source and a scanning mirror.
 24. The method of claim 15 wherein the composite image includes at least one of the cornea, iris, pupil, shape of the pupil, sclera, or blood vessels in the sclera. 